Organic materials have recently shown promise as the active layer in organic based thin film transistors and organic field effect transistors [see H. E. Katz, Z. Bao and S. L. Gilat, Acc. Chem. Res., 2001, 34, 5, 359]. Such devices have potential applications in smart cards, security tags and the switching element in flat panel displays. Organic materials are envisaged to have substantial cost advantages over their silicon analogues if they can be deposited from solution, as this enables a fast, large-area fabrication route.
The performance of the device is principally based upon the charge carrier mobility of the semi-conducting material and the current on/off ratio, so the ideal semi-conductor should have a low conductivity in the off state, combined with a high charge carrier mobility (>1×10−3 cm2 V−1 s−1). In addition, it is important that the semi-conducting material is relatively stable to oxidation, i.e., it has a high ionisation potential, as oxidation leads to reduced device performance.
A known compound which has been shown to be an effective p-type semiconductor for OFETs is pentacene [see S. F. Nelson, Y. Y. Lin, D. J. Gundlach and T. N. Jackson, Appl. Phys. Lett., 1998, 72, 1854]. When deposited as a thin film by vacuum deposition, it was shown to have carrier mobilities in excess of 1 cm2 V−1 s−1 with very high current on/off ratios greater than 106. However, vacuum deposition is an expensive processing technique that is unsuitable for the fabrication of large-area films.
It is an aim of the present invention to provide new materials for use as semiconductors or charge transport materials, which are easy to synthesise, have high charge mobility, good processability and improved oxidative stability. Other aims of the invention are immediately evident to those skilled in the art from the following description.
The inventors have found that these aims can be achieved by providing new monomers, oligomers and polymers based on azulene.

Azulene is a non-benzenoid aromatic hydrocarbon which is planar and thermodynamically stable. Polymerisation at the 2- or 6-position results in a linear structure. As a result, polyazulenes pack closely, thus exhibiting a higher degree of order that leads to particularly high charge carrier mobility. Furthermore, by adding alkyl chains and other substituent groups to the azulene core, the azulenes can be made more soluble thus being suitable for spin coating or solution coating techniques, rather than vacuum deposition, to prepare thin films for use, e.g., in electronic devices such as transistors.
1,3-Polyazulenes (A) have been prepared electrochemically, as reported by K. Iwasaki et al, Synth. Metals, 1995, 69, 543 and Y-B. Shim et al, J. Electrochem. Soc., 1997, 144, 3027 and M. Porsch et al in Adv. Mater., 1997, 9, 635, and by stirring in strong acid, as reported by N. Kihara et al, J. Amer. Chem. Soc., 1997, 30, 6385. Azulene appended cellulose has also been reported [see F. X. Redl et al, Macromol. Chem. Phys., 2000, 201, 2091]

Copolymers of azulene have also been reported. DE 34 25 511, DE 3929383 and DE 39 38 094 disclose a copolymerisate of pyrrole and azulene obtained by electrochemical polymerisation in the presence of sulfonic acid and a conducting salt. DE 44 45 619 discloses a copolymer with azulene and phenylene units linked by phenylmethylene groups.
However, polyazulenes polymerised at the 2- and 6-position according to the present invention have not been reported.
Another aspect of the present inventions relates to advantageous uses of the mono-, oligo- and polyazulenes, including their oxidatively or reductively doped forms, according to the invention.